关键词: 离子液体基质, 寡糖, 糖肽, 三羟基苯乙酮, 质谱

Matrix plays a fundamental role in the desorption/ionization process during MALDI MS analysis, thus is closely related to the spectral quality. Nevertheless, it is usually difficult for analytes to disperse homogeneously due to the formation of hot spots, which had become a problem encountered with many of the current matrices. This may result in increased measurement time and hamper the application of MALDI MS. Although many efforts have been devoted to optimize matrix choice for oligosaccharide and glycopeptides analyses, there are few matrices that could work well with them in MALDI MS so far. In this study, a novel class of ionic liquid matrices (IMs) based on trihydroxyacetophenone (THAP) was introduced as potential alternatives to the traditional crystalline matrices and showed superior performance for oligosaccharides and glycopeptides analysis. The combination of pyridine or N,N-dimethylaniline (DMA) with 2',3',4'-trihydroxyacetophenone (2',3',4'-THAP) or 2',4',6'-trihydroxyacetophenone (2',4',6'-THAP) at the molar ratio of 1:1 turned out to be well suited for the analysis of oligosaccharides. Besides, the optimized condition could be achieved by 5-fold dilution of the IMs and adding ammonium citrate dibasic[(NH₄)₂HCit] as matrix additive. Afterwards, in comparison to signals obtained with traditional solid matrix 2,5-dihydroxybenzoic acid (DHB), substantial improvements in sensitivity were observed by the new IMs. Specifically, signal-to-noise ratios of dextran1000 as well as β-cyclodextrin were enhanced more than 10-fold. Moreover, the complex glycan mixture from the intact glycoprotein of RNase B released by PNGase F could be detected with high sensitivity when 2',3',4'-THAP/DMA functioned as the matrix. The unbiased nature of such IM also made it applicable to analyze glycopeptides derived from 10 ng tryptic digests of horseradish peroxidase (HRP), while it was almost impossible to detect any signals when measured with solid matrix 2',3',4'-THAP. In comparison to methods involving derivatization of oligosaccharides, which are susceptible to contamination and often require tedious purification steps, such technique could be readily used and largely reduce sample losses during analysis. As a consequence, these new IMs are promising to be advantageous in glycosylation analysis by MALDI-TOF MS.

Key words: ionic liquid matrix, oligosaccharides, glycopeptides, trihydroxyacetophenone, mass spectrometry